Testing systems are commercially available to test the harmonic distortion and frequency response of hearing aids. Such a conventional test system is disclosed in U.S. Pat. No. 3,922,506, in the name of the present applicant, and it teaches the use of a microphone coupler between the sound pressure chamber and the signal processing and indicating means.
Conventional microphone couplers are provided with an artificial ear cavity of a prescribed volume which communicates with a bore in which a condenser microphone is sealingly positioned. Several types of microphone couplers are needed in order to test the various kinds of hearing aids.
These conventional forms of couplers have been recommended by the American National Standards Institute (ANSI) to test the various forms of hearing aids, but these couplers while capable of providing reproducible results, do not satisfactorily provide good measurement means for checking new hearing aid developments, such as, venting of ear molds and the use of all-in-the-ear hearing aids.